The invention relates generally to a cooling system for an imaging system and, more particularly, to a wicking structure for a cryogenic cooling system in a magnetic resonance imaging (MRI) device.
Imaging devices, such as magnetic resonance imaging (MRI) devices, are typically used to diagnose patients in medical environments. The generated magnetic resonance image is a map of weak magnetization originated from the atomic nuclei in the body tissue as influenced by presence of an external magnetic field. By detecting these influences, MRI devices produce detailed images of a patient's internal tissues and organs, thereby enabling diagnosis of disease, injuries, among other physiological conditions of a patient.
In the traditional MRI system, the superconductive electromagnet has a number of loops of coiled wire that are bathed in a cryogenic fluid, such as liquid helium. This cryogenic fluid cools the coiled wire to extremely low temperatures, maintaining the magnet in a superconducting state. Cryogenic cooling system employed for cooling the imaging device components utilize abundant amount of the cryogenic fluid to provide localized cooling, thereby increasing the cost and also the complexity of the system. Thermal insulating material and other heat transfer barriers, such as vacuum regions, are often provided to insulate the magnet and cryogenic fluid, to impede heat transfer between the magnet and the environment.
Unfortunately, cryogenic systems, such as MRI systems, utilize large amounts of coolant, for example, about 1000 to 2000 liters of Helium, to provide localized cooling to the superconducting coils and cryogenic vessel walls. The coolant required in conventional cryogenic systems is very costly. Current systems use excess amount of helium to maintain the magnet in its superconducting state at all times. In current machines the annular cavity between the superconducting magnet and the inner cryogenic vessel walls are filled with liquid helium, commonly fully or partially submerging the superconducting magnets. During operation, a small amount of heat can be generated at the surface of a partially-submerged superconducting magnet coil and a fraction of the total liquid helium volume is boiled off. In addition, even though the cryogenic vessel containing the superconducting magnet uses superior insulation, a small amount of heat from the outside will conduct into the cryogenic vessel causing additional liquid helium boiloff.
In general, the MRI device is topped off with liquid helium at the factory where it is produced and then shipped to the customer, which could be anywhere around the world. During this transportation process, typically a significant greater amount of liquid helium is lost. At arrival at the customer site, the machine is topped off again with liquid helium. Due to availability and scarcity of high purity liquid helium at different locations in the world this might be very costly. Therefore, reducing the total liquid helium amount of the cryogenic vessel is beneficial.